Fire-fighter training

ABSTRACT

A fire simulator comprises fuel distribution means under a grating through which fuel emanating from the fuel distribution means can rise in use to create flames extending above the grating, wherein the grating includes a plurality of grating elements that together define a walkable working surface for a fire-fighter using the simulator.

BACKGROUND OF THE INVENTION

This invention relates to fire-fighter training. In particular, theinvention relates to fire-fighter training installations such as thoseused to simulate fires in aviation scenarios, notably those of aircraftcrash-landings.

The invention is not limited to aviation fire-fighting scenarios: it hasapplication in simulators for other fire-fighting scenarios such as roador railway crashes that, like an aircraft crash-landing, can involve asubstantial fuel spill. Indeed, preferred aspects of the inventioninvolve simulators that can be adapted for a variety of different firesimulations not necessarily involving fuel spillage, including aircraft,collapsed buildings, road-vehicles, trains and multiple-scenarioincidents. Such simulators can also be used for ‘joint services’training, i.e. to train members of other emergency services, notably thepolice and paramedics, who must co-ordinate their work withfire-fighters from time to time.

Speed and skill are of the essence to all fire-fighters butfire-fighting in aviation scenarios, such as aircraft crash-landings,requires particularly fast response and skilled teamwork if loss of lifeis to be minimised. It is generally accepted that unless a burningcrash-landed aircraft is accessed and the fire suppressed within twominutes of ignition, there is little hope of survival for those on boardwho may have survived the landing itself. As there is so little time formistakes, this places extraordinary demands upon the skill offire-fighters based at civil airports and military airbases. There arecorresponding demands upon the training of those fire-fighters, both asindividuals and as a team, and hence upon the quality of the simulatorson which those fire-fighters practice.

All substantial airports and airbases have dedicated fire tenders onstandby for substantially immediate high-speed access to any crash sitewithin the airport or airbase perimeter. Such tenders include vehiclesknown in the art as Major Airport Crashtrucks or MACs. Upon approachingthe stricken aircraft, the practice is to drive the tenders close to theaircraft for the purpose of laying down fire-retardant foam andsimultaneously gaining access to the fuselage of the aircraft to freeits passengers and crew. Indeed, recent practice in civil aviationfire-fighting is to drive a specially-adapted tender right up to theaircraft for the purposes of puncturing its fuselage and injecting foamto protect people who may still be alive within.

Of course, accidents are characterised by their unpredictability andthere is no way of knowing what difficulties fire-fighters willencounter when they reach a crash-landed aircraft. Their fire-fightingstrategy must therefore be fully flexible. For example, the orientationof a burning aircraft with respect to the prevailing wind will have aconsiderable influence upon how the fire-fighters can approach theaircraft, suppress the fire and access the fuselage. Also, obstructionssuch as airport vehicles and broken-off engines, undercarriagecomponents, wings or other parts of the aircraft can block access to thefuselage and will, in all likelihood, be on fire themselves. This is allquite apart from the different types of aircraft fire with whichfire-fighters must contend: a fire confined to an engine or theundercarriage, for example, will require a quite different strategy to afire involving spilled fuel.

The demands of fire-fighter training have led to the emergence offire-fighting simulators in which fluid-fuelled flames are controlled torespond realistically to efforts by trainees to suppress them, inso-called ‘hot-fire’ training. Aviation fire simulators are typicallysited at an airfield or airbase, close to the fire-fighters' base atthat facility. Flame generators can extend across the ground to simulatea fuel spill and can also be associated with mock-ups of above-groundstructures associated with a fire scenario, such as a metal tuberepresenting a section of aircraft fuselage which may have structuresrepresenting wings and engines to one or both sides, or a metal boxrepresenting an airport vehicle. In an analogy apt for acting-outscenarios, these mock-ups are referred to in fire-fighter training as‘props’. That term will be used hereafter in this specification whenreferring to such mock-ups.

In early days, the fuel used in aviation fire simulators was liquid fuelsuch as oil or jet fuel but whilst their flames are realistic inappearance, those fuels give rise to levels of pollution that would beunacceptable today in frequently-used simulators that are often situatednear urban settlements. Consequently, there has been a move towardgas-fuelled simulators and here the challenge is to maintain realism andcontrollability.

The aim of any fire simulator is to mimic the behaviour of a flame as itdevelops from ignition to eventual extinction. Spilled liquid fuel burnsin a similar manner to the same fuel in an open-topped tank. Uponignition, the height of the flames is initially quite small. However,the flames progressively grow larger and spread quickly across the fullarea of the spillage, eventually reaching a limiting height determinedby the burning velocity of the flame. The flame grows during this phasebecause its radiant heat promotes the evaporation of liquid fuel. Theincreased rate of evaporation causes the flame to grow and this appliesadditional radiant heat to the remaining liquid fuel, increasing therate of evaporation still further until the burning velocity of theflame prevents further flame growth.

Reference is made at this point to FIG. 1, whose source is Drysdale, D.An Introduction to Fire Dynamics, 2^(nd) edition, p. 12, published in1998 by John Wiley & Sons. This is a schematic representation of aburning surface showing the heat and mass transfer processes involved incombustion. Importantly, it shows that in all fire occurrences, heatflux supplied by the flame (Q_(F)″) transfers to the fuel surface. Thisheat transfer then increases the volatility of the fuel, hence adding tothe conflagration.

Clearly, therefore, a key aspect of simulating a liquid fuel spill fireis to transmit radiant heat to liquid fuel so as to promote theevaporation of that liquid fuel.

An example of a gas-fuelled fire-fighting simulator is disclosed in U.S.Pat. No. 5,055,050 to Symtron Systems, Inc., which comprises a diffusersuch as a pan filled with a bed of dispersive medium such as water orgravel in which a burner system comprising a network of perforated pipesis submerged or buried. The pipes carry pressurised liquefied petroleumgas (LPG)—preferably propane—which is initially in its liquid phase but,with reducing pressure, flashes into the vapour phase within the pipesas it approaches the holes in the pipes. Thus, the pipes contain a mixof vaporising liquid propane and propane vapour. The gas issuing fromthe pipes diffuses as it rises through the dispersive medium and thenburns on the surface of the dispersive medium. Two or more pans can beused side-by-side.

Whilst such use is not specifically disclosed in U.S. Pat. No.5,055,050, it is well known in the art that the flames can be controlledto respond appropriately to the trainee fire-fighters' actions. Forexample, the fuel flow rate in different parts of the network of pipesor in different pans can be varied under central control via remotevalves. It is also known that the pans can be used beside a prop such asa mock aircraft fuselage to lend further realism to training scenarios.

The simulator arrangement of U.S. Pat. No. 5,055,050 enjoys certainbenefits such as low cost and is suitable for many trainingrequirements, but the exposed bed of the dispersive medium causesseveral problems that the present invention seeks to overcome.

One of the major problems of an exposed bed is that the dispersivemedium lacks structural integrity and can bear no significant load. Thismeans that props cannot be supported on the bed and that vehicles cannotdrive over the bed without risking fracture of the pipes underneath thesurface and so possibly causing a genuine conflagration. It follows thatareas of the simulator are artificially off-limits to fire tenders and,for safety reasons, have to be delineated as such with markers orbarriers that extend beyond the forbidden area.

Given the reliance upon close approach of fire tenders to aircraft inaviation fire scenarios, it is hugely unrealistic to prevent tenders, intraining, accessing areas of the simulator installation that, in ananalogous real fire, correspond to areas around an aircraft upon whichthe tender would advantageously be driven. This problem is particularlyacute given that tenders must be driven artificially gently and slowlyduring training to avoid accidentally driving onto the forbidden areas:in real life, their drivers will approach an accident site at thehighest possible speed and brake as hard and late as they can. It issimilarly unrealistic to have to place props beside rather on top of thebed, where the simulated fire is raging.

Another disadvantage of the exposed bed of dispersive medium is thatprops cannot be dragged across the bed if it is desired to rearrangetheir position: they can only be lifted into place by a crane. Thislimits the adaptability of the simulator by increasing the cost andtimescale of any changes in the orientation or layout of the props, suchas may be necessary to track changes in wind direction, if indeed suchchanges are possible within the confines imposed by the extent of thebeds surrounding the location of the prop. Aside from developingfire-fighting skills applicable to different situations, the ability tovary training scenarios is important to maintain the trainees' interestand focus.

There is also the problem that fire-fighter trainees cannot walk safelyon the bed of dispersive medium as they fight the simulated fire: even ashallow pan of water is self-evidently unsuitable for access on foot,and the alternative medium of gravel or other particulate refractorymaterial presents a trip hazard that could cause a trainee to stumbleinto the flames. This drawback further deprives the simulator ofrealism, because, in real life, fire-fighters will expect to advance onfoot as they fight back the flames whereas, when using the simulator,their advance will be limited by the margins of the bed.

Yet another drawback of the exposed bed of dispersive medium is that themedium can be disturbed by the flow of water used by traineefire-fighters to simulate foam. That flow typically reaches 11,000litres per minute from each nozzle used to fight the fire. Where thedispersive medium is a particulate medium such as gravel, for example,such a powerful jet of liquid can wash the gravel about within the pan,removing gravel from some parts of the pan and piling it up elsewhere inthe pan. At best, this varies the depth of the bed of gravel to thedetriment of optimal dispersion and combustion of the fuel rising fromthe perforated pipes. The behaviour of the simulator may therefore varyunpredictably from one training exercise to the next, unless the gravelis raked back into a level layer between those exercises. At worst,sections of the pipes can be exposed, depriving the out-flowing fuel ofany dispersive effect and exposing the pipes to the full radiant heat ofcombustion.

The present invention seeks to solve these problems and therefore toextend the use of gas-fuelled simulators into other parts of thesimulator market, providing a simulator in which the realism of trainingis as great as can be allowed by the safety of those who operate andtrain on it.

SUMMARY OF THE INVENTION

Broadly, the invention resides in a fire simulator comprising fueldistribution means under a grating through which fuel emanating from thefuel distribution means can rise in use to create flames extending abovethe grating, wherein the grating includes a plurality of gratingelements that together define a walkable working surface for afire-fighter using the simulator. It is further preferred that theworking surface can be driven upon by a fire-fighting vehicle such as afire tender or a Major Airport Crashtruck without damaging the fueldistribution means, and that such a vehicle can drive on and off theworking surface from and onto a surrounding or neighboring apron. Thesefeatures of the invention enable realistic fire-fighting training bymaking the flames and related scenarios fully accessible tofire-fighters on foot or in a vehicle.

The aim of the invention is further assisted if the working surface isaligned at its periphery with a surrounding or neighbouring apron. Tothis end, the fuel distribution means is advantageously housed in arecess below the grating, the recess having a base below the level ofthe surrounding or neighbouring apron. There may be a pan in the recesscontaining the fuel distribution means.

The grating elements may be supported by grating supports that standbeside the fuel distribution means below the grating elements. Thosegrating supports can space the grating elements from the fueldistribution means. For easy assembly and reconfiguration, especially insecondary incident training scenarios, the grating elements arepreferably removable from the grating supports and more preferably cansimply be lifted away from the grating supports and out of the workingsurface.

The grating supports are elegantly defined by a plurality of hollowsupport frames, each of which can include upright peripheral wallssurrounding a central cavity. For example, the walls can be in arectangular or square arrangement around a correspondingly-shapedcavity. The walls of the frame lie against the base of the recess or thepan in use and so preferably have lower edge portions shaped to define adrainage opening. Upper edge portions of the frames can be shaped toreceive an array of grating elements that bridge the cavity so that thearray defines a portion of the working surface. For instance, the upperedge portions may be castellated. The support frames are suitably laidin intersecting rectilinear arrays with walls of neighbouring framesaligned with and facing one another. Fixing plates attached to the loweredge of walls of the frame may then provide for fixing the frame to afoundation or base such as the base of the aforementioned recess.

The support frames are preferably arranged such that a plurality ofgrating elements are disposed in a parallel array across the cavity. Inthat case, where the support frames are laid in a row, the orientationsof grating elements in neighbouring frames of that row are preferablymutually orthogonal. This helps to dissipate the kinetic energy ofincoming jets of water and so minimises outwash of any particulatematerial associated with the fuel distribution means under the grating.

To accommodate thermal expansion without distortion, it is advantageousfor the grating elements to be movable to a limited extent with respectto the support frame. Elegantly, movement of the grating elements can belimited by encountering a neighbouring support frame.

The invention can be applied to various burner arrangements includingthose in which the fuel distribution means is buried, submerged orexposed. Thus, for example, the fuel distribution means may be coveredby a fuel-dispersive medium from which dispersed fuel rises through thegrating. In that case, the fuel-dispersive medium can be accommodated inthe cavities of an array of support frames to define a bed extendingunder the working surface that is subdivided by the walls of thosesupport frames.

It is also possible for the fuel distribution means is associated withfuel-heating means for applying to the fuel distribution means radiantheat that emanates from the flames in use, thereby promotingvaporisation of liquid fuel in the fuel distribution means. Thefuel-heating means can absorb radiant heat emanating from the flames andthen radiate to the fuel distribution means some of the heat thusabsorbed. The fuel-heating means can also reflect some of the radiantheat emanating from the flames.

The simulator of the invention can further include a service trenchbeing surrounded by or bordering the working surface that includes amovable or removable access cover lying flush with the working surface.That cover can be vented to permit free venting of gases from theservice trench and where the service trench contains control equipmentfor lighting and fuelling the flame, the trench preferably defines wallshaving cavities into which the control equipment is recessed forprotection from heat and water. The service trench can also drainfire-fighting water or rainwater that runs through the grating.

It is greatly preferred if the grating elements remain below 200 Celsiusin use, as this is the usually threshold for the use of standardfire-fighter personal protection equipment such as footwear.

The simulator of the invention enables a prop to be supported by itsworking surface, and for the prop to be moved across the working surfacewhile being supported by the working surface.

This International patent application claims priority from theApplicant's United Kingdom Patent Application Nos. 0005012.0, 0014311.5and 0102569.1, the contents of which are incorporated herein byreference. Those applications are not continuing in their own right asthey refer to prototype development but copies of them are available onthe public file of this application, from the date on which thisapplication is published. The discussion of flame characteristics andtheir testing and analysis set out particularly in Application Nos.0005012.0 and 0014311.5 may be of background interest to readers of thisspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more readily understood, referencewill now be made, by way of example, to the accompanying drawings, inwhich:

FIG. 1, which has already been described, is a diagram of a burningsurface;

FIG. 2 is a schematic sectional side view of a fuel spill simulator inaccordance with a first embodiment of the invention;

FIG. 3 is a perspective view of a serpentine array of fuel distributionpipes being part of the first embodiment of the invention;

FIG. 4 is a schematic sectional side view of a fuel spill simulator inaccordance with a second embodiment of the invention;

FIG. 5 is a schematic sectional side view of a fuel spill simulator inaccordance with a third embodiment of the invention;

FIG. 6 is a perspective view of an array of support frames laid overserpentine arrays of fuel distribution pipes, as part of the thirdembodiment of the invention;

FIG. 7 is a perspective view corresponding to FIG. 6 but showing gravellaid over the fuel distribution pipes within all of the support framesand grating bars laid on some of those support frames over the gravel;

FIG. 8 is an enlarged perspective view of one of the support frames ofFIG. 7, with the grating bars partially cut away to show gravel withinthe frame and that gravel being partially removed to show a fueldistribution pipe normally buried by the gravel;

FIG. 9 is a perspective part-sectioned view of part of the array ofsupport frames bordering the central trench of FIG. 5, showing theirdrainage provisions;

FIG. 10 is a schematic perspective view of a substantially completesimulator corresponding to FIG. 5;

FIGS. 11(a) and 11(b) are schematic plan views of a simulatorcorresponding to that shown in FIGS. 5 and 10, showing how a prop suchas a mock-up aircraft can be positioned and re-positioned on the workingsurface;

FIG. 12 is a partial schematic perspective view of a simulatorarrangement suitable for Secondary Incident Training (SIT) scenarios;

FIG. 13 is a partial schematic perspective view of the simulatorarrangement of FIG. 12, but showing a SIT prop on the working surface ofthe simulator and enabled for use; and

FIG. 14 is a schematic plan view of a simulator having a main prop andshowing locations for siting auxiliary SIT props used to enact variousSIT scenarios.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 2 of the drawings, in a first embodiment ofthe invention, a fuel spill simulator 1 comprises a steel pan 2 set intoconcrete foundations 3 that support the pan 2. The pan 2 may, forexample, be circular or rectangular in plan, and is bordered by servicetrenches 4 that contain control equipment 5 and services such as fuelsupply pipework and power or control cabling (not shown). The trenches 4shown in FIG. 2 may, of course, represent opposed sections of onecontinuous trench 4 that surrounds the pan 2.

The pan 2 and the trenches 4 are surmounted by a grating 6 that definesa flat, level working surface on which a trainee fire-fighter can walkand upon which a fire-fighting vehicle can preferably drive. Fulldetails of the grating 6 will be given later. In the embodimentillustrated, the working surface defined by the grating 6 extends beyondthe trenches 4 into neighbouring or surrounding areas 7 on the otherside of the trenches 4 from the pan 2, which areas may surmountneighbouring pans of similar design. In any event, the grating 6 shouldbe flush with the neighbouring or surrounding areas 7 to minimise triphazards and will eventually extend to a contiguous concrete apron orblockwork surface (not shown) with which it preferably defines acontinuous substantially level surface.

The base of the pan 2 is dished slightly to promote drainage offire-fighting water W or precipitation through a central drain 8, fromwhich the water W is preferably filtered and recycled. The pan 2supports a layer of gravel 9 of substantially uniform thickness and aplurality of vertical grating supports 10 that support the grating 6 atintervals across its width over the pan 2. The supports 10 extend fromthe grating 6 to the pan 2 and so extend through a mesh 11 over thegravel 9 such that their base portions are surrounded by gravel 9. Itwill be evident that in view of the dished shape of the pan 2, thesupports 10 are of various lengths to suit their position with respectto the centre of the pan 2, while keeping the grating 6 level.

Exposed fuel distribution pipework 12 constituting a burner extends overthe gravel layer 9 and the mesh 11 and around the supports 10 in asinuous, serpentine array. The pipes 12 of the array are preferably ofmaintenance-free stainless steel. As can be seen in FIG. 3 which showsan array of pipes 12 over the pan 2 but omits the intermediate gravellayer 9 for clarity, the pipes 12 are perforated to definedownwardly-facing orifices, holes or nozzles for the egress of propanesupplied from a supply pipe 13 leading from control equipment 5 withinthe trench 4 beyond the outer edge of the pan 2. The propane is in theliquid phase under pressure before it enters the pipes 12, but flashesinto the vapour phase as it flows through the pipes 12 before itsemergence from the orifices, holes or nozzles in the pipes 12, whereuponthe gas streams downwardly to approach the gravel layer 9.

During its journey through the pipes 12, a mix of propane vapour andswiftly-vaporising liquid propane is warmed by the radiant heat to whichthe pipes 12 are exposed. This promotes the evaporation of the remainingliquid fraction and the flammability of the fuel as a whole, whichbeneficially simulates the behaviour of a real fuel spill. The radiantheat radiates downwardly from the flames above the grating 6 andupwardly from the gravel layer 9, this latter radiation being due toreflection of radiant heat that originated from the flames, and heatingof the gravel layer 9 itself by that heat. The openings of the grating 6are large enough to permit substantial radiant heat flux to pass throughthe grating 6, but not so large as to present a trip hazard forfire-fighters walking on the working surface defined by the grating 6.

As can be seen in the enlarged detail view included in FIG. 2, an arrayof parallel or intersecting rods 14 sandwiched between the gravel 9 andthe pan 2 act as groynes to resist movement of the gravel 9 with respectto the pan 2, especially down the slope of the dished pan base. Wherethe rods 14 intersect, they are preferably interlaced in woven manner todefine openings for water drainage down the dished shape of the pan base2. Retention of gravel 9 is further assured by the aforementioned wiremesh 11 that lies on top of the layer of gravel 9 under the fueldistribution pipework 12. Once heated in use, that mesh 11 can furthercontribute to the upwardly-radiating heat that warms the fueldistribution pipes 12 and the propane streams emanating from those pipes12.

The enlarged detail view included in FIG. 2 also makes plain that thegravel 9 comprises various particle sizes. To be specific, the stonespecification is of igneous rocks selected from the following group ofclassifications, namely: fine-grained granite; diabase; gabbro; basalt;and rhyolite. The stone is crushed and provided as sized aggregateconforming to ASTM-C33, grade 2 (or equivalent), as follows:

Sieve Size (nm) 100% 75 90-100% 65 35-70%  50 0-15% 40 0-5%  20

As can be seen in FIGS. 2 and 3, each trench 4 beside the pan 2 containsa fuel supply control unit for regulating the supply of fuel to the fueldistribution pipes 12 and a pilot control unit for lighting the fuelejected from the pipes 12, which units are shown together as controlequipment 5 hung on a side wall of the trench 4. The trench 4 is closedin use by a porous lid 15 under the grating 6 (omitted from FIG. 3),which lid serves to protect the control equipment 5 from radiant heatbut can be opened to afford access to the control equipment 5 whenrequired. The trench 4 also contains an air pipe 16 whose purpose is topurge the trench 4 of flammable and potentially explosive gases that maybuild up in use, when the trench 4 is closed by the lid 15. The air pipe16 does this by introducing air to pressurise the trench 4: this helpsto prevent dangerous contaminants entering the trench 4 and forcesexcess air together with any contaminants out of the trench 4 throughthe porous lid 15.

The embodiment of FIG. 4 is broadly analogous to that of FIGS. 2 and 3in that it provides for full vaporisation of fuel by downward projectionabove gravel 9, so like numerals are used for like parts. The keydifferences are that, in FIG. 4:

-   -   the pan 2 is cambered so that water runs outwardly from the        centre and drains into the trench(es) 4;    -   the supply pipes 13 that supply the fuel distribution pipework        12 are centrally located with respect to the pan 2, inboard of        the fuel distribution pipework 12, rather than being at the        outer edge of the pan 2;    -   the trenches 4 lack lids and so are open in the sense that they        vent freely to atmosphere through vented covers 17; and    -   the control equipment 5 is recessed into cavities in the trench        wall for protection from heat and water.

The relative simplicity of the FIG. 4 embodiment will be evident uponcomparing the drawings, which reduces its cost in comparison with theFIG. 2 embodiment but without sacrificing performance. Specifically, thetrenches 4 perform the dual function of housing and providing access tothe control equipment 5 and also draining water from the pan 2. Thisobviates the central dedicated drain 8 of FIG. 2. Furthermore, the opentrench design provides inherent explosion relief without the need forthe purging air pipes 16 of FIG. 2. Being recessed into the trench wall,the control equipment 5 no longer needs the protection of the porous lid15 from radiant heat, but it will need to be positioned above themaximum water level that is predicted to be in the trench 4 under themaximum flow rate of incoming water W in use. It will also be apparentthat the inboard supply pipes 13 that supply the fuel distributionpipework 12 can be shorter and simpler than the outboard supply pipes 13of FIG. 2.

The embodiment of FIG. 5 also shares some features with the embodimentsof FIGS. 2 and 4 and so again, like numerals are used for like parts.Unlike the embodiments of FIGS. 2 and 4, there is no pan; instead, asteel-edged recess is simply formed in a concrete slab foundation 3 tocontain a layer of gravel 9. A typical depth for this recess would be upto 500 mm but this depends on the drainage requirements and what thetotal finished area of the simulator might be.

The gravel 9 is surmounted by a grating 6, preferably lying flush withthe surrounding concrete or blockwork apron 18, that stands on verticalsupports 10 extending upwardly from the base of the recess. In thisembodiment, a trench 4 extends centrally along the recess and, as shownin the enlarged detail view included in FIG. 5, the fuel distributionpipework 12 lies on the base of the recess and so is disposed below thegravel layer 9. Again, the pipework 12 is perforated to define a seriesof holes, apertures or nozzles to eject fuel in use, but unlike theembodiments of FIGS. 2 and 4 which eject fuel downwardly for maximumevaporative effect, the fuel of the FIG. 5 embodiment can be ejected inany direction as it is intended to be dispersed by the gravel 9 in anyevent.

As in FIG. 4, the trench 4 of the FIG. 5 embodiment is closed by avented cover 17 so as to vent explosive gases to atmosphere and thecontrol equipment 5 is recessed into cavities in the trench walls. Also,whilst no camber or dish is evident from FIG. 5, the base of the recessis very gently inclined, sloped or dished toward the trench 4 to promotedrainage of water from the gravel layer 9. It is advantageous that waterdoes not drain away too quickly, so as to allow enough time for theflare-off of unburned gas; otherwise, that unburned gas may be entrainedin a fast-moving stream of water and swept away to cause dangerous gasaccumulations downstream.

To describe the grating 6 and its supports 10 in detail, the descriptionof the FIG. 5 embodiment will now continue with reference to theremaining drawings. It will be evident to the skilled reader how thegrating 6 and supports 10 shown in those drawings can be adapted to suitthe embodiments of FIGS. 2 and 4 in which, unlike FIG. 5, the fueldistribution pipework 12 is exposed above the gravel layer 9. Inparticular, it will be readily apparent how most if not all of thegrating features of the FIG. 5 embodiment can be applied to thepreceding embodiments if a suitably adapted support is used.

Referring then to FIGS. 6 to 9 of the drawings, the abovementionedgrating supports 10 are defined by the upstanding walls 10A, 10B offabricated square support frames 20 that are open to their top andbottom and that lie upon and are fixed to the base of the recess of FIG.5. As best shown in FIGS. 6 and 7, the support frames 20 fit together inrectilinear arrays in mutually-abutting modular fashion, so that eachsupport frame 20 helps to support its neighbours against side loadingsin use. The walls 10A, 10B of the various support frames 20 thus lie inorthogonally-intersecting vertical planes.

Looking at any one of the support frames 20 as shown in FIG. 8, it willbe noted that each of its four walls 10A, 10B is a flat elongate platethat is preferably of mild steel. Each plate is welded at each of itsopposed ends to a respective orthogonally-disposed neighbouring plate,the welded junctions between the plates thus defining the corners of thesquare between the walls. Additionally, each plate has a cut-out 21extending along one of its long edges, namely the lower edge that isdisposed generally horizontally and facing downwardly in use. The endsof the cut-outs 21 are defined by feet 22 that have a square fixingplate 23 welded to them at the lower corners of the support frame 20.Each fixing plate 23 is therefore arranged to lie flat against the baseof the recess and it is pierced by a through-hole (not shown) thatenables the support frame to be bolted or otherwise fixed to the base.Whilst not essential, it is preferred that the support frames 20 arefixed down in this way so as to prevent excessive sideways movement or‘shuffling’ of the support frames as vehicles drive over the workingsurface of the simulator.

The cut-outs 21 in the walls of the support frames 20 align with thoseof neighbouring support frames 20 in use, and have the dual function ofaccommodating the serpentine arrays of fuel distribution pipes 12previously fixed at appropriate locations to the base of the recess, andof permitting water W to drain across the base of the recess toward thecentral trench of FIG. 5. Specific reference is made to FIG. 9 in thisrespect.

The plates defining two opposed walls 10B of each support frame arefurther provided with castellated upper edges defined by a row ofupstanding oblong teeth 24 alternating with, and delineated by, oblongslots 25. As will be most apparent from FIGS. 7 and 8, the purpose ofthe castellations is to hold a set of oblong-section steel grating bars26 bridging the open top of the support frame 20 in a parallel spacedarray that defines a substantially flat, if locally slightly inclined,working surface level with the upper edges of the walls 10A, 10B and theteeth 24. Thus, the castellations hold the grating bars 26 at a suitableheight above the fuel distribution pipes 12, and keep those bars 26 inthe correct position during use of the simulator.

To this end, each grating bar 26 is held at one end in a slot 25 of onecastellated wall 10B and at the other end by the corresponding slot 25of the opposite castellated wall 10B. It will also be apparent from thedrawings that the major cross-sectional axis of each grating bar 26 isoriented vertically to maximise its load-bearing ability against loadsmoving over the grating 6.

In practice, the grating bars 26 are fitted into the slots 25 only afterthe aforementioned layer of gravel 9 in the form of igneous stonechippings or other particulate dispersive medium has been poured intothe open support frames 20 around the fuel distribution pipes 12,burying them to a depth of say 120 mm. The layer of gravel 9substantially fills the space around the fuel distribution pipes 12between the grating bars 26 and the base of the recess. It will beapparent that the gravel 9 has little room to move when so positionedand that any tendency it might have to shift sideways across the recessis limited by the baffle effect of the walls 10A, 10B that effectivelypartition the gravel bed 9.

It will also be noted, with particular reference to FIGS. 6, 7 and 10,that neighbouring support frames 20 in rows or columns of the arraywithin the recess are turned through 90° with respect to each other sothat their castellated walls 10B never abut one another. Thus, as bestshown in FIG. 10, the grating bars 26 define cells 27 in rows or columnscorresponding to the support frames 20 and the grating bars 26 ofadjacent cells are mutually orthogonal. This alternating arrangement canbe appreciated in the check pattern extending over the working surfaceof the simulator.

The functional significance of the alternating arrangement of thegrating bars 26 is twofold. Firstly, the grating bars 26 are free toslide longitudinally within their slots 25 for the purposes of thermalexpansion without distortion but once they have slid to a limited extent(a maximum of 10 mm in the preferred embodiment), they will bear againstthe non-castellated wall 10A of a neighbouring support frame 20 and socan slide no further. This is important under the dynamic sideways loadslikely to be imparted by a swerving or braking fire tender or otheremergency vehicle. Secondly, a major benefit of the grating 6 is itsability to dissipate the flow of incoming jets of water or otherfire-fighting agents and so to prevent the dispersive medium beingdisturbed by those jets being played directly on the working surface ofthe simulator. As the dissipating effect of a straight grating of whollyaligned elements might conceivably be overcome if the incoming jet isaligned with the elements, the alternating arrangement of grating bars26 has the benefit that it will reliably disrupt jets of water strikingthe working surface from any angle. In any event, any water that doesget through the working surface while retaining damaging momentum willbe dissipated by the baffle effect of the walls 10A, 10B between thesupport frames 20, under the working surface.

To help visualise the size of each frame 20, and strictly by way ofexample only, their pitch or spacing between centres is nominally 1metre and so the overall width of each frame is 990 mm square to leave athermal expansion gap of 10 mm all round. The walls 10A, 10B of eachframe are 25 mm thick and stand a total of 200 mm above the base of therecess. Each grating bar 26 is of 80 mm×30 mm black bar and the slots 25that receive the grating bars 26 are of corresponding dimensions. About170 mm is therefore available under the grating bars 26 and above thebase of the recess to accommodate the fuel distribution pipes 12 and thesurrounding layer of gravel 9. The spacing between neighbouring gratingbars 26 of a given support frame 20 is no greater than 33 mm so as topresent no trip hazard to trainee fire-fighters walking on the workingsurface. The pitch or spacing between centres of the grating bars 26 istherefore nominally 66 mm and there is provision for thirteen of suchbars 26 on each support frame 20.

A grating specified as above can withstand the maximum wheel load of aMajor Airport Crashtruck (MAC). Performing structural analysis accordingto the requirements of BS5950:Part1:1985 using ANSYS 5.0A, and assuminga mass of the tender of 501.1 kN and a maximum axle load of 130 kN, thegrating can comfortably withstand braking from 20 kph.

Moreover, the considerable mass of the grating bars 26 (in the order of250 kg/m²) imparts thermal inertia that makes them slow to attaindamaging temperatures. During typically short bursts of use from cold(anything longer than three minutes of practice fire-fighting is rare inview of the need for extreme speed in real-life aviation fire-fighting),their temperature keeps well within the parameters appropriate toordinary personal protection equipment (PPE) routinely worn byfire-fighters. Fire-fighter protective footwear and other PPE is ratedto withstand temperatures up to 200 Celsius; tests show that the mass ofthe grating bars 26 keeps their temperature to about 180 Celsius evenafter exposure to the radiated heat flux of a fire with flametemperatures between 700 and 1100 Celsius.

A beneficial side-effect of the considerable girth of the grating bars26 is that corrosion will not significantly reduce their cross-sectionand hence load-bearing strength during their projected working life.Consequently, the working surface of the simulator needs no expensive orfragile corrosion treatments, and is essentially maintenance-free.

The load-bearing ability of the working surface is heightened by theelegant design of the fabricated support frames 20, in which downwardloads are transferred directly to the foundations through the verticalwalls 10A, 10B without putting the aforementioned welds under damagingtensile or bending loads.

As already mentioned, the embodiment shown in FIG. 5 et seq is modularin nature. Specifically, it is envisaged that a standard modulecomprises a serpentine fuel distribution pipe 12, an associated fuelsupply control unit and nine support frames 20 in a 3×3 array and hence,with the above dimensions, gives a working surface that covers 9 m².Several such modules can be used together to construct a simulatorhaving a working surface of any required size, such as the one shown inFIG. 10 which comprises eight modules on each side of the central trench4, giving a total working area of 144 m² excluding the area of thetrench 4 itself. In practice, the working area of a simulator willgenerally be substantially greater so that large props can be placed onthe working surface and correspondingly wide-ranging fuel spills can besimulated.

The central trench 4 featured in FIGS. 5, 9 and 10 is covered by aremovable vented cover 17 as shown in FIGS. 5 and 10, which can belifted when it is necessary to gain access to the control equipment 5and ancillary equipment, such as valve trains and service pipework,within the trench 4.

FIGS. 11(a) and 11(b) show how a prop 28, in this case a mock-up of amilitary jet, can be placed freely on the working surface of a simulatorakin to that of FIG. 10. In both drawings, the prop 28 is aligned withthe prevailing wind shown by the arrows as this is the direction inwhich a crash-landed aircraft is most likely to lie, although otherangles to the prevailing wind can obviously be simulated forwide-ranging practice. In FIG. 11(a), the prevailing wind is offset byabout 30° with respect to the central trench 4 of the simulator and thecentral longitudinal axis of the prop 28 is similarly aligned. Howeverin FIG. 11(b), the prevailing wind is aligned with the trench 4 and theprop 28 has been re-aligned accordingly and also advanced across theworking surface. Highly advantageously, the prop 28 can simply bedragged across the working surface from one orientation to the other,with no need of a crane to lift the prop 28.

Moving on finally to FIGS. 12, 13 and 14, these drawings illustrate afurther embodiment of the invention suitable for fire-fighter traininginvolving so-called secondary incidents. Specifically, a main or primaryincident—for example, an aircraft crash landing—could well beaccompanied by one or more secondary incidents such as a collapsedbuilding hit by the aircraft or a burning airport vehicle set alight bya fuel spill from the aircraft. Training for that kind of eventuality isknown in the art by the acronym SIT, standing for Secondary IncidentTraining.

The embodiment of FIGS. 12, 13 and 14 caters for SIT by providing one ormore locations on and under the working surface of the simulator thatcan be adapted to enable the use of one or more secondary props inparallel with, or instead of, a main prop. This is achieved by theprovision of a channel 30 formed in the base 31 of the recess, whichchannel 30 extends from the central trench 4 under the fuel distributionpipes 12 to a desired location under the working surface. The channel 30itself is best shown in FIG. 12, whereas FIG. 13 shows the channel 30filled with service supply links 32 (such as a pilot fuel duct, a mainflame fuel duct and control/electronics cabling) and terminating in aSIT control unit 33 to which those service supply links 32 run. In thisway, each channel 30 contains the services necessary to fuel and controla small SIT scenario.

In normal use of the simulator with a main prop (not shown), the servicesupply links 32 and the SIT control unit 33 remain dormant under thegrating 6, which continues to present an uninterrupted working surface.Indeed, the fuel distribution pipes 12 remain undisturbed and so, withsuitable heat-shielding, the service supply links 32 and the SIT controlunit 33 can be left buried under gravel 9 for the purposes of normalfire simulation, burning fuel supplied via the fuel distribution pipes12 at that location.

When a SIT scenario is to be enacted, a small SIT prop 34 (in this case,resembling a car that will simulate a small vapour fire) is draggedacross the working surface to near the location of the SIT control unit33. The service supply links 32 and the SIT control unit 33 can then beenabled simply by removing sufficient grating bars 26 (which lift outeasily from their castellated support frames 20) and underlying gravel 9to gain access to the SIT control unit 33, whereupon the flexibleconnections 35 necessary to bring pilot fuel, main fuel, control signalsand electrical power to the nearby SIT prop 34 can simply be pluggedinto the SIT control unit 33. The flexible connections 35 can beshrouded by a protective sleeve (not shown) if they are exposed toflame, as they will be in FIG. 13, although some SIT props may makeprovision for internal connection to the SIT control unit 33 in such away that the prop itself shields the connections from the flames.

Only one channel 30 is illustrated in FIGS. 12 and 13 for the purposesof clarity. However, for optimum flexibility, there are preferably a fewsimilarly-equipped channels 30, such as four of them, leading todifferent locations dispersed around the working surface of thesimulator. Such an arrangement is shown in FIG. 14 in which a main prop36 representing a full-size Boeing 747-400 aircraft, which is optionallya permanent fixture, has extensive fuel spill simulators 37 to the portand starboard sides. Here, four locations for possible SIT scenarios arerepresented as blocks 38. One example could be a SIT prop fabricated torepresent a re-fuelling tanker servicing the aircraft and so locatednear a wing 39, and a multi-scenario training exercise could begin withan incident with the tanker, escalating to a fuel spill fire, escalatingto a larger fuel spill fire and finally involving the aircraft itself.The simulated fire could spread to, or the scenario could otherwiseinvolve, other SIT props at other locations on the working surface ofthe simulator.

In general, the props can be moved, swapped and interchanged with greatflexibility to create fresh training scenarios involving interactionbetween a main incident, a fuel spill and one or more secondaryincidents, that can be adapted readily to suit the prevailing weatherand the needs of the trainees. This fosters the ability to set up ‘jointservices’ training involving combinations of fire, police and paramedicservices, and ensures that scenarios remain instantly controllable sothat if, for example, a genuine incident occurs during training, crewscan break off from training and attend that incident without delay.

Many variations are possible within the inventive concept. For example,whilst a gravel bed is preferred as a dispersive medium where such amedium is to be used, the grating of the invention could alternativelybe used over a pan of water acting as the dispersive medium.Consequently, reference should be made to the appended claims and toother conceptual statements herein rather than to the foregoing specificdescription in determining the scope of the invention.

1. A fire simulator comprising fuel distribution means for distributingfuel under a grating through which fuel emanating from the fueldistribution means can rise in use to create flames extending above thegrating, wherein the grating includes a plurality of grating elementsthat together define a walkable working surface for a fire-fighter usingthe simulator and wherein the working surface can be driven upon by afire-fighter vehicle without damaging the fuel distribution means, whichvehicle can drive on and off the working surface from and onto asurrounding or neighbouring apron.
 2. The fire simulator according toclaim 1, wherein the working surface is aligned at its periphery withthe surrounding or neighbouring apron.
 3. The fire simulator accordingto claim 1, wherein the fuel distribution means is housed in a recessbelow the grating, the recess having a base below the level of thesurrounding or neighbouring apron.
 4. The fire simulator according toclaim 3, wherein a pan in the recess contains the fuel distributionmeans.
 5. The fire simulator according to claim 1, wherein the gratingelements are supported by grating supports that stand beside the fueldistribution means below the grating elements.
 6. The fire simulatoraccording to claim 5, wherein the grating elements are removable fromthe grating supports.
 7. The fire simulator according to claim 6,wherein grating elements can be lifted away from the grating supportsand out of the working surface.
 8. The fire simulator according to claim5, wherein the grating elements are spaced from the fuel distributionmeans by the grating supports.
 9. The fire simulator according to claim5, wherein the grating supports are defined by a plurality of hollowsupport frames.
 10. The fire simulator according to claim 7, whereineach support frame includes upright peripheral walls surrounding acavity.
 11. The fire simulator according to claim 10, wherein walls ofthe frame have lower edge portions shaped to define a drainage opening.12. The fire simulator according to claim 10, wherein walls of the framehave upper edge portions shaped to receive an array of grating elementsthat bridge the cavity, the array defining a portion of the workingsurface.
 13. The fire simulator according to claim 10, wherein thegrating elements are movable with respect to the support frame.
 14. Thefire simulator according to claim 13, wherein the grating elements moveuntil they encounter a neighbouring support frame.
 15. The firesimulator according to claim 1, wherein the fuel distribution means iscovered by a fuel-dispersive medium from which dispersed fuel risesthrough the grating.
 16. The fire simulator according to claim 15,wherein support frames each include upright peripheral walls surroundinga cavity and the fuel-dispersive medium is accommodated in the cavityand defines a bed extending under the working surface subdivided by thewalls of a plurality of support frames.
 17. The fire simulator accordingto claim 1, wherein the fuel distribution means is associated withfuel-heating means for applying to the fuel distribution means radiantheat that emanates from the flames in use, thereby promotingvaporisation of liquid fuel in the fuel distribution means.
 18. The firesimulator according to claim 17, wherein the fuel-heating means absorbsradiant heat emanating from the flames and radiates to the fueldistribution means some of the heat thus absorbed.
 19. The firesimulator according to claim 17, wherein the fuel-heating means reflectssome of the radiant heat emanating from the flames.
 20. The firesimulator according to claim 17, wherein the fuel-heating means includesa layer of particulate refractory material.
 21. The fire simulatoraccording to claim 20, wherein a foraminous sheet or mesh is interposedbetween the fuel distribution means and the layer of particulaterefractory material.
 22. The fire simulator according to claim 1 andbeing arranged such that the grating elements remain below 200 Celsiusin use.
 23. The fire simulator according to claim 1 and including a propsupported by its working surface.
 24. The fire simulator according toclaim 23, wherein the prop can be moved across the working surface whilebeing supported by the working surface.
 25. A fire simulator comprisingfuel distribution means for distributing fuel under a grating throughwhich fuel emanating from the fuel distribution means can rise in use tocreate flames extending above the grating, grating supports that standbeside the fuel distribution means below and support an array of gratingelements and are defined by a plurality of hollow support frames eachcomprising upright peripheral walls surrounding a cavity, the walls ofthe frame having castellated upper edge portions shaped to receive thearray of grating elements that bridge the cavity and comprise a portionof a walkable grating working surface for fire-fighters using thesimulator.
 26. The fire simulator according to claim 25, wherein thewalls are in a rectangular or square arrangement around acorrespondingly-shaped cavity.
 27. The fire simulator according to claim26, wherein the support frames are laid in intersecting rectilineararrays with walls of neighbouring frames aligned with and facing oneanother.
 28. The fire simulator according to claim 25, wherein aplurality of grating elements are disposed in a parallel array acrossthe cavity.
 29. The fire simulator according to claim 28, wherein thesupport frames are laid in a row and wherein the orientations of gratingelements in neighbouring frames are mutually orthogonal.
 30. A firesimulator comprising fuel distribution means for distributing fuel undera grating through which fuel emanating from the fuel distribution meanscan rise in use to create flames extending above the grating, thegrating comprising a plurality of grating elements that together definea walkable working surface for a fire-fighter using the simulator andgrating supports that stand beside the fuel distribution means below anarray of grating elements and are defined by a plurality of hollowsupport frames each comprising upright peripheral walls surrounding acavity, wherein fixing plates are attached to the lower edge of thewalls of the frames to provide for fixing the frames to a foundation orbase.
 31. A fire simulator comprising fuel distribution means fordistributing fuel under a grating through which fuel emanating from thefuel distribution means can rise in use to create flames extending abovethe grating, wherein the grating includes a plurality of gratingelements that together define a walkable working surface for afire-fighter using the simulator and wherein the grating elementscomprise a plurality of separate elongate bars each having at least oneface that defines part of the working surface when the bar is orientedgenerally horizontally for use.
 32. A fire simulator comprising fueldistribution means for distributing fuel under a grating through whichfuel emanating from the fuel distribution means can rise in use tocreate flames extending above the grating, wherein the grating includesa plurality of grating elements that together define a walkable workingsurface for a fire-fighter using the simulator and the simulator furthercomprises a service trench surrounded by or bordering the workingsurface and including a movable or removable access cover that liesflush with the working surface.
 33. The fire simulator according toclaim 32, wherein the cover is vented to permit free venting of gasesfrom the service trench.
 34. The fire simulator according to claim 32,wherein the service trench contains control equipment for lighting andfuelling the flame, and defines walls having cavities into which thecontrol equipment is recessed.
 35. The fire simulator according to claim32, wherein the service trench drains fire-fighting water or rainwaterthat runs through the grating.